We discovered that oligodendrocytes in the midbrain and hindbrain express high levels of the glutamate metabolizing enzyme glutamine synthetase (GS). In addition to this striking observation, we also detected functional glutamate transporter currents in midbrain oligodendrocytes, thus demonstrating that oligodendrocytes can both take up and metabolize extracellular glutamate. As such, they are in a position to regulate the concentration and localization of extracellular glutamate, which may have implications for both excitatory synaptic transmission as well as protection from excitotoxicity. We are now crossing a floxed GS mouse line with an oligodendrocyte-specific cre line to determine whether oligodendrocyte GS is required for proper regulation of extracellular glutamate.